How to make solar power 24/7

Aug 01, 2011

Diagram shows the idealized arrangement of a vat of molten salt used to store solar heat, located at the base of a gently-sloping hillside that could be covered with an array of steerable mirrors all guided to focus sunlight down onto the vat.
Image: Courtesy of Alexander Slocum et al.

The biggest hurdle to widespread implementation of solar power is the fact that the sun doesn't shine constantly in any given place, so backup power systems are needed for nights and cloudy days. But a novel system designed by researchers at MIT could finally overcome that problem, delivering steady power 24/7.

The basic concept is one that has been the subject of much research: using a large array of mirrors to focus sunlight on a central tower. This approach delivers high temperatures to heat a substance such as molten salt, which could then heat water and turn a generating turbine. But such tower-based concentrated solar power (CSP) systems require expensive pumps and plumbing to transport molten salt and transfer heat, making them difficult to successfully commercialize  and they generally only work when the sun is shining.

Instead, Alexander Slocum and a team of researchers at MIT have created a system that combines heating and storage in a single tank, which would be mounted on the ground instead of in a tower. The heavily insulated tank would admit concentrated sunlight through a narrow opening at its top, and would feature a movable horizontal plate to separate the heated salt on top from the colder salt below. (Salts are generally used in such systems because of their high capacity for absorbing heat and their wide range of useful operating temperatures.) As the salt heated over the course of a sunny day, this barrier would gradually move lower in the tank, accommodating the increasing volume of hot salt. Water circulating around the tank would get heated by the salt, turning to steam to drive a turbine whenever the power is needed.

The plan, detailed in a paper published in the journal Solar Energy, would use an array of mirrors spread across a hillside, aimed to focus sunlight on the top of the tank of salt below. The system could be "cheap, with a minimum number of parts," says Slocum, the Pappalardo Professor of Mechanical Engineering at MIT and lead author of the paper. Reflecting the system's 24/7 power capability, it is called CSPonD (for Concentrated Solar Power on Demand).

The new system could also be more durable than existing CSP systems whose heat-absorbing receivers cool down at night or on cloudy days. "It's the swings in temperature that cause [metal] fatigue and failure," Slocum says. The traditional way to address temperature swings, he says: "You have to way oversize" the system's components. "That adds cost and reduces efficiency."

The team analyzed two potential sites for CSPonD on hillsides near White Sands, N.M., and China Lake, Calif. By beaming concentrated sunlight toward large tanks of sodium-potassium nitrate salt  each measuring 25 meters across and five meters deep  two installations could each provide 20 megawatts of electricity 24/7, which is enough to supply about 20,000 homes. The systems could store enough heat, accumulated over 10 sunny days, to continue generating power through one full cloudy day.

While exact costs are difficult to estimate at this early stage of research, an analysis using standard software developed by the U.S. Department of Energy suggests costs between seven and 33 cents per kilowatt-hour. At the lower end, that rate could be competitive with conventional power sources.

The team has carried out small-scale tests of CSPonD's performance, but its members say larger tests will be needed to refine the engineering design for a full-scale powerplant. They hope to produce a 20- to 100-kilowatt demonstration system to test the performance of their tank, which in operation would reach temperatures in excess of 500 degrees Celsius.

The biggest challenge, Slocum says, is that "it's going to take a company with long-term vision to say, 'Let's try something really different and fundamentally simple that really could make a difference.'"

Most of the individual elements of the proposed system  with the exception of mirror arrays positioned on hillsides  have been suggested or tested before, Slocum says. What this team has done is essentially an "assemblage and simplification of known elements," Slocum says. "We did not have to invent any new physics, and we're not using anything that's not already proven" in other applications.

Gershon Grossman, who holds the Sherman-Gilbert Chair in Energy at the Technion-Israel Institute of Technology, says this approach "includes several innovative CSP concepts." But, he adds, "the main advantage of this system is its ability to deliver power continuously, unlike other CSP systems, which are affected by clouds. This work is innovative and is expected to make a significant contribution" to the industry, he says.

Slocum emphasizes that this approach is not intended to replace other ways of harvesting solar energy, but rather to provide another alternative that may be best in certain situations and locations. Playing on the familiar saying about rising tides, he adds, "A rising sun can illuminate all energy harvesters."

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User comments : 52

The molten salt approach to continue producing power during the night isn't novel (see Andasol powerplants in Spain), but I like the setup because it reduces one problem: If you have prolonged times of no sunshine then the saltsolidifies. In a tank this isn't a problem but current solar/salt powerplants have extensive pipes through which the salt is pumped. If the salt solidifies in these pipes then it's very hard to get going again (worst case: you have to thaw the salt using fossil fuels or downright replace the plumbing or keep heating the salt mixture artificially during the low solar power days)

yes, that is exactly correct. The other thing about the systems with all that piping is the corrosive nature of the high temperature salts. The expected lifespan of the pipes is extremely short when looking at it from the perspective of cost over time. One more thing here is that it takes a fairly skilled maintenance staff to keep one of these things running, which means that you have to get a handfull of skilled people who are willing to work in places that are usually way out in the middle of nowhere. It may seem like a small problem but it isn't trivial.

These technologies will continue to get cheaper, but for now they are still in infancy. The spare parts are still custom items, with different plants using different parts, and people educated and qualified to run them are specialists. It may be 20 years or more before the industry reaches critical mass, it it lasts that long before becoming obsolete due to something better. That's a risky investment.

Wasn't there an article on Physorg recently about the Spanish plant already running for 48 straight hours taking a similar approach to the problem?

The Spanish plant, and others like it, are what is called a "power tower" arrangement. The liquid salt is stored in a huge underground tank, and a small amount of liquid salt is circulated to the top of the tower, then heated and returned to the tank in a continuous loop. It's a very technically complicated process with lots of moving parts, such as valves and pumps. There are expensive filters which wear out, seals which wear out, expansion and contraction from heating and cooling which causes massive strain on the whole system (the length of a pipe will change dramatically when you heat it, for example). The system described above is a VASTLY simpler system, if it performs as advertised. They are basically heating the salt directly in the storage tank, therefore eliminating the most complicated parts. It's really brilliant.

This is exactly the kind of work that makes MIT so freaking cool. I'm just sayin'.

The geometric arrangement of the mirrors is interresting. It will raise alarm bells for environmentalists. It's probably safe to assume that natural formations do not occur in perfect eliptical bowls facing south very often. So, you're going to have to move a lot of earth to make one of these, and it's going to be on the scale of a big strip mine or mountain-top removal process. You could minimize the evils and try to use mountaintop removal sites and other existing excavations, and convert them to this purpose after the mining is done, I would guess. It's still going to leave a got-awefull gaping hole in the ground covered in mirrors.

On a side note, actively tracked mirrors are problematic too. Maintenance is really high. Keeping them free of dust, animal stuff, and trimming brush around them is a lot of work too. The big plant in Germany is all overgrown. Mirrors too low to mow under. Bad plan.

Yeah, hydrogen from sea water may become a competitive alternative. There are several technical roadblocks that are keeping it off the market though. For stationary power generation it's just too costly to compete at the scale needed. For portable power the problem depends on which system design you're talking about. Ideally, you don't want a soccer mom driving around in a minivan full of kids, and trust her to safely operate and maintain a hydrogen system. As with the current generation gas engine, there would be accidents as safe methods and user education go through the learning curve. If our society wasn't so lawsuit crazy, then maybe somebody could do it though. There's lots of stuff in that quandry, such as computer driven cars. The long term benefits outweigh the short term certainty of accidents, but who takes the risk? Investors and insurors aren't willing at the present risk/reward level. continued

If you invested a pile of money into something like hydrogen fuel cells, it's highly unlikely that you'd ever get a return. Even if you are relatively certain that the technology will go viral, there's still the question of which brand to put your money into. For example if you had invested in a social media startup before facebook took off, if had chosen any social media company besides facebook, then you would have lost. Most people in the tech world knew that social media would be the next big killer app. But which startup would gain critical mass? HD DVD versus BluRay is another example of two great ideas in a market space that will only tollerate one. Power supply and distribution is like that to an extent too. You geometrically increase the cost every time you split the market between additional competition. Any good hydrogen system needs to be good enough to replace an existing system, not supplement it. It sucks, but that's economics.

For example if you had invested in a social media startup before facebook took off, if had chosen any social media company besides facebook, then you would have lost.

HD DVD versus BluRay is another example

That's not really an apt analogy since facebook profiles and other profiles (or BluRay and HDD) aren't interchangeable. But hydrogen manufactured via method X and hydrogen manufactured via method Y is. It's only a bad choice if you go for method X and method Y outperforms you by a substantial amount.

The metal coating industry has been safely using molten salts for decades. I don't think that's an issue at all. I think there are several types that would be viable. A hybrid system is also possible. You could actively heat one type of salt, then use a heat exchanger to transfer the energy to another type of salt in the storage tanks. That way you could maximize the efficiency at each step. Solid carbon is another option for bulk heat storage, though that makes the heat exchange complicated.

On a side note, there was a story about 15 years ago about a guy, in England I think?, who fell off a catwalk into one of those molten salt vats at a metal treatment plant. He managed to crawl out of the tank on his own and he survived. Can you imagine? All of his small body features were basically gone.

But hydrogen manufactured via method X and hydrogen manufactured via method Y is. It's only a bad choice if you go for method X and method Y outperforms you by a substantial amount

That's true to some extent, but you are oversimplifying. Not only does the process need to be profitable, but it also needs to remain profitable for the full time needed to repay your capital investments. Five years or longer is typical. HD DVD is an example where it did not last long enough.

For hydrogen there are multiple options for production, transport, storage, distribution, and consumption. If you set up a company which produces bulk hydrogen at the coast in preperation for an infrastructure where you deliver trucks of hydrogen to filling stations, then the industry standard becomes based on transporting sea water through pipelines and converting the hydrogen locally, then you are cut out of the logistics flow. Or if you are committed to a standard, you could be regulated out.

There are myriad examples where a particular method of doing something would be perfectly viable, but it only makes sense to choose one of two good ideas. Society doesn't even always pick the best choice as the standard. AC versus DC current is an example of that. Broadcasting standards, internet protocols, railroad guage sizes, Windows OS, etc. At this stage of the renewables game, there are a lot of moving parts in the investment puzzle. If you build a hydrogen conversion plant, but nobody makes any hydrogen cars, what do you do? What if they only make 100,000 of them and they all get shipped to Denmark? What if you are using a particular catalyst and the only major supplier in the world cuts off the supply? See what I mean now?

I believe they were looking at using a dry solid form of carbon, probably in combination with other materials in the form of some kind of ceramic blocks. I don't think that method has much traction right now. You would need to run pipes down into it with heat exchangers for both heat input and heat extraction. With any of these liquid salt systems, you still need to get the heat back out to run industry standard turbines, which means that you are constrained to a certain temperature range on the output side. It's not the biggest issue, but it's one of those things that constantly locks you down in other areas, such as the temp range of your storage tank. That has a domino effect all the way up the chain to the size of your mirror field and its minimum density and minimum average sunlight exposure.

I'll bet thermodynamics would understand this better than I do. The size and nature of the components in a system like this are not arbitrary. You can't just use any size and shape tank you want, for example. It all depends on what temperature range you want to maintain, and what the heating properties of your storage medium are like. Different materials will behave differently at certain temperatures, and there's a relationship between your temperatures and your efficiency at different stages of the process. It's all interconnected. If this MIT scheme is viable, then it's really a big deal. I don't think most people really understand how big, in terms of the engineering. They've really cut out a LOT of crippling constraints if their system really can eliminate the whole tower.

Not only does the process need to be profitable, but it also needs to remain profitable for the full time needed to repay your capital investments.

yes, but depending on how cheap the upkeep of the plant is that's not really a problem. Havong vats of algae produce hydrogen or putting to leads into water which are powered by a solar power plant basically have (next to) no running costs. Amortization times will differ depending on setup costs, but both will eventually pay for themselves no matter the efficiency. You can make a suboptimal choice when choosing which you invest in, but you can't make a choice that won't get you your money back.

Transportation is a good argument, though. Going for trucks is not a huge hazard since that is how hydrogen is transported already - and you can switch over if need be.

I'd basically set this up in Africa and use ships as transport. Makes you independent of the market.

Amortization times will differ depending on setup costs, but both will eventually pay for themselves no matter the efficiency. You can make a suboptimal choice when choosing which you invest in, but you can't make a choice that won't get you your money back.

That isn't true. You must pay interest on your capital, in addition to any fixed costs such as property taxes, employee wages, building maintenance, accounting, etc. The interest on the capital is the big one though. If you're making your product at a cost that allows you to make a profit, but a competitor is making the same product at a lower cost and selling it for a price that does not allow you to make a profit, then you will go out of business. You can't repay the capital if you are not able to sell your product. That's very basic economics. You can't sell hydrogen, or any other product, above the market value.

I'd basically set this up in Africa and use ships as transport. Makes you independent of the market.

How does that make you independent of the market? You still have to sell your product, which is done on the market. Well, since you seem to think that this stuff can make money, even when you have to sell it for less than it costs to make it, why not just give it away. Then you're free of the market. You could just release it into the amosphere and let anyone who wants collect it back up. The wind could carry it around the world for everyone to have. lol. I'm kidding of course. Seriously, transporting a product over long distances creates a huge expense, especially a product that is not very dense in terms of dollars per unit of volume. Hydrogen is much less valuable than oil on a dollars per cubic foot basis. Transporting it is also very dangerous. It requires a special truck, and here in the US, they have escort cars in front and back, along approved routs only.

That's why I said that as long as you make (any) profit you're 'safe'. Whether someone can undercut your price depends on many things (and not only the price of manufacturing the goods).

If, for example, I manufacture hydrogen in Africa for a certain price and you manufacture hydrogen in India for less then transportation costs may still make my plant profitable in Africa (or anywhere where I have short enough supply lines, advantages in tarrifs/customs, ...)

An example would be oil production which is much more costly in some areas than in others:Multi billion dollar oil rigs still seem to turn a healthy profit despite Saudi oil wells being a dime a dozen (by comparison).

A ship full of hydrogen would not be allowed into any port here in the US, and probably not anywhere else either. Not a chance. Never happen. You could never get a license to run a hydrogen pipeline either. Lol, your idea of a hydrogen transport ship is hillarious. Can you imagine a ship the size of an oil tanker, but needing to refridgerate the whole thing? Half the ship would be compressors and heat exchangers. You'd need an army of mechanics to keep it running, and god help you if you get a leak somewhere.

Funny how you can actually buy unrefrigerated, compressed hydrogen in (red) cylinders and transport it anywhere you want without a license or special safeguards (even in the US). Any school will have those in their chemistry lab.

And I'm willing to bet large sums of money that such cylinders are sometimes even transported by ships which make harbor in the US.

An example would be oil production which is much more costly in some areas than in others:Multi billion dollar oil rigs still seem to turn a healthy profit despite Saudi oil wells being a dime a dozen (by comparison)

And yet, oil refineries go out of business all the time. In your imaginary scheme, that wouldn't be possible. In reality, making money isn't good enough unless you make enough money to repay your initial investment. You are pretending that the rate at which you repay it is irrelevant, but that's not true either. Loans have payment schedules. You MUST make your payments on time, or they close you down. Have you ever borrowed money before? This is a simple concept. To run a business where you borrow money from investors to build it, you can't just make a little bit of money and call it good. The margin on hydrogen would be very small, so anybody with a better process would push you out of the market in an instant. Then you're screwed. Investors don't like that.

Funny how you can actually buy unrefrigerated, compressed hydrogen in (red) cylinders and transport it anywhere you want without a license or special safeguards (even in the US). Any school will have those in their chemistry lab.

And I'm willing to bet large sums of money that such cylinders are sometimes even transported by ships which make harbor in the US

Oh good lord, that's not the same at all. Bulk storage and transport is an entirely different animal. Those cylinders you're talking about are orders of magnitude less compressed than what you need for large scale industrial hydrogen. Those cylinders you are talking about don't contain enough hydrogen to run a car for hardly any time at all. You would need a trailer full of those to equate to a tank of gasoline.

The plants in question would produce the stuff - not refine it.And since you have already ascertained that transportation is a problematic (and expensive) factor then location should be the thing when it comes to whether a plant is profitable or not (and not how it produces the stuff).

Look, I'm not making stuff up. I'm simply listing the real world reasons that it is currently difficult to obtain funding for alternate energy pilot projects, or any other type of pilot project for that matter. These reasons are well-known. It's basic stuff. That's why you usually see pilot projects funded mainly with taxpayer money, and usually in association with a University, or several Universities.

Transportation is a problem, but it's hard to say what the biggest problem is. It takes a LOT of electricity to electrolyze seawater. You could use wind turbines, but that's stop and go power. Wave or tide power would be best. That's problematic from the ecological point of view though. You'll have Greenpeace taking you to court. The other big problem is the Chlorine byproduct that is difficult to get rid of. As for your suggestion, locating a seawater plant away from the coast would be a bad idea.

I can see from your comments that you don't really understand the hydrogen from seawater concept very well. I would suggest doing a lot more reading on the subject. Such a plant is in reality a type of refinery. They would produce hydrogen, oxygen, and some type of alkali or chlorine waste. The process of seperating the hydrogen gas from the oxygen gas is a refining process. You would be operating a chemical refinery. Look up the term "refinery" and you'll see what it means. There's no point in me talking to you about this stuff if you won't look up the basics before you disagree with me.

Depends on where you put it. Off shore it's mostly go in a lot of areas.

Wave or tide power would be best. That's problematic from the ecological point of view though. You'll have Greenpeace taking you to court.

Greenpeace didn't lift a finger against the Limpet type powerplant. Those can be constructed so unobtrusively as to be undetectable. Haven't seen them sue against off shore tidal plants, either.

It takes a LOT of electricity to electrolyze seawater

there's a lot of ways to get at hydrogen. Algae/electrolysis was just an example. Even so: rather than dump excess energy during very sunny or windy days it would be OK to use electricity to create hydrogen.

As for your suggestion, locating a seawater plant away from the coast would be a bad idea.

This is purely accademic though. It's much cheaper to make hydrogen from natural gas, and it doesn't look like it will become cheaper to use seawater any time soon. You're dreaming if you think hydrogen from seawater could make money with current methods. Good luck replacing PLATINUM anodes all the time. lol.

This is true as long as producers don't have to foot the bill for environmental impact (same goes for nuclear, gas and coal for that matter). If we ever run into a major global environmental crisis - which we might - then we can expect to see a change here.

By weight, Hydrogen is energy rich - However, by volume in it's gaseous state, is is energy poor

Yeah, in fact it takes as much as 5% of your potential energy just to compress it down to a reasonable level. It's so impractical to do anything with the hydrogen that's produced by electrolysis, that it's usually just burned off as a waste product (which turns it back into water, lol). The hydrogen is just not worth enough to bother trying to save it.

This is true as long as producers don't have to foot the bill for environmental impact (same goes for nuclear, gas and coal for that matter).

Producers don't foot the bill, consumers do. We've already beaten the subject of carbon taxes to death though. Do we really have to talk about that again? We were having a nice little non-political discussion about technology and you had to play the political card? I'll keep my agenda in its box if you'll keep yours in a box for now too. :)

The article here is talking about a method to produce green energy which is actually close to being competitive. I was just responding to your suggestion of hydrogen because I think it's an interesting topic too. If they can fix the platinum anode problem, it might be really cool, but it's just such a gosh darn inefficient process. There's so much waste byproducts and energy loss from heat, plus additional processing costs after production. It's really a loser tech for now.

Hydrogen cannot be made competitively (With fossil fuel) price wise. However, it is close enough that it may become competitive on an on site basis, but not at a distance

Are you suggesting that you create hydrogen then burn it in some kind of engine or boiler system to create electricity at a power plant? Why not just use the input electricity before you do the electrolysis, and forget about the middle steps? The only reason you'd EVER want to use hydrogen for energy production is for portable power, like a car. It takes more energy to make hydrogen than you get back out of it (waste, byproducts and extra processing), so unless you're using it remotely there's no point.

Which is true of every renewable, portable power carrier (otherwise you'd have a perpetuum mobile)

We've already beaten the subject of carbon taxes to death though. Do we really have to talk about that again?

I don't know - I have never had a talk on carbon taxes (on this site or anywhere else). The point is that the only reason that a hydrogen economy (currently) isn't competitive is because of an artificially skewed market. But basically I don't care whether it's gonna be hydrogen or batteries or whatever other clean/renewable energy carrier. The hydrogen argument was made by holoman. I just thought your attack on it was (and is) flawed (as is his idea of generating hydrogen from seawater for that matter).

However, as a separate issue, your point about the artificially skewed market is somewhat true. Every major energy industry is subsidized in the US, often at several places (From putting down oil wells in TX, hiring men, all the way to Exxon taking the oil and refining it.)

I think we need to stop subsidizing profitable industries, so that when we subsidize a new industry, it will actually do some good. Any energy industry has to be subsidized in the US, just to have a fair market, and that is ridiculous.

Which is true of every renewable, portable power carrier (otherwise you'd have a perpetuum mobile)

Good one. That's funny and clever, but not accurate. Making gasoline does not require more energy than you get back out. You can actually run an oil refinery on only a small portion of the plant's output, so the end product has WAY more energy than what it takes to make it. Most experts say that making ethanol from corn is very nearly an even trade, or maybe slightly on the positive side. Hydrogen is way over on the negative side of the energy in/out equation. Chemical batteries are also very energy negative. Even solar panels and windmills are tough because they both take a lot of energy to build, install and maintain. It takes a long time to recover all the calories expended in making them. If the balance is negative it's not sustainable. You can't use batteries to run a battery plant. I wonder if windmills are positive or negative over thier lifespan, which is short.

Making gasoline does not require more energy than you get back out. You can actually run an oil refinery on only a small portion of the plant's output,

You're not manufacturing petrol products out of thin air in a refinery. The energy is already in the crude oil you pour in.

Note also that I said: "renewable" energy carrier. Oil is not renewable. *

*OK, you can manufacture oil from scratch but that process is way, way, WAY more inefficient to use as an energy carrier than going for hydrogen.

Ethanol from corn (and oil) are false analogies because there you have already a lot of energy in it at the outset (put in there by the sun). If yopu conveniently omit that then that is not surprisingly 'more efficient' than hydrogen.

To cite some numbers from there: Wind powerplants give you, on average, 19 times the energy back that you put in to make them. Which comes out as an energetic amortisation time of under 6 months depending on size - see third table. Economic amortisation time is around 10 years. For the worst typ of alternative powerplant (PV) -see second table- energetic amortization is between 2 and 5 years.

For energetic amortisation nuclear, oil and coal plants are, on average, much worse than wind (worse even than solar thermal or hydro and just barely better than PV). If you include the energy need for the primary fossil fuels then those conventional plants don't even break even (naturally...or you'd have a perpetuum mobile again).

They would produce hydrogen, oxygen, and some type of alkali or chlorine waste.

That actually is true. I make my own bleach for my laundry by electrolyzing seawater (or, in the absence of that, add salt to tap water) just for fun. Its murder on the electrodes, though. Avoid stainless steel. I ran out of graphite sticks and ended up using a couple kitchen knives in a pinch. I ended up dissolving much of the knives and having to filter a lot of blackened mess out of my mixture by the time I got done. I imagine electrode replacement could get very expensive over time.

Its murder on the electrodes, though. Avoid stainless steel. I ran out of graphite sticks and ended up using a couple kitchen knives in a pinch. I ended up dissolving much of the knives

The best thing they have right now is platinum for the anode and carbon for the cathode, as far as I know. Since platinum is more expensive than gold, it does tend to be a little costly.

Antialias: The following is a report from a conservation group, the John Muir Trust. They did a study of real world wind farm performance, and compared it to the claims made by sources such as your wiki page link. Enjoy:

The actual performance of wind farms falls significantly short of what is commonly spouted by pro-windfarm activists such as yourself. Keep in mind that the report I just linked to was done by a pro-environmental group, not some skeptic or big oil flunky.

"At the end of the period studied, the connected capacity of wind power was over 2500MW so the expectation is that the wind network will produce, on average, 750MW of energy. In fact, it's delivering far less than everyone's expectations. The total wind capacity metered now is 3226MW but at 3a.m. on Monday 28th March, the total output was 9MW."

I can see where this is going.

But all the numbers they cite in the lower part seem to be OK. They don't support the 'conclusions' though.

Example: 124 times low power for average of 4.5 hours in a 2 year period. And then they say that that is not 'infrequent' as the environmentalists claim. Hello? That's 3% of the time. What is the definition of 'infrequent' in their books?

Then they say: UK pumped hydro storage runs out in 22 hours. Well with average of 4.5 hours 'outage' that is plenty of time. (European grid also does not mean you have to limit yourself to UK hydro storage capacities.)

You must be joking right- why make a closed system an open one that also needs desalinization steps and ontop of that you have to cope with the energy hit making hydrogen gas.

Even as silly I think using salts for thermal storage is- it is still more efficient in terms of storing energy then lith-ion batteries. Hell the thermos you might bring soup for lunch at work is more efficient at storing energy then a lith-ion battery...

Hell the thermos you might bring soup for lunch at work is more efficient at storing energy then a lith-ion battery...

That really depends upon what you do to the battery on initial charge. Experience has shown me that a lithium-ion battery will store more energy and last longer if you allow it to charge fully and leave it in the charger for at least 24-48 hours before first discharging it. I have found that if used right away out of the box, the battery will tend to charge up to the point where you stopped the charge on initial use. I have found this to be the case for laptops, ipods, and just about everything I have ever used that had a lithium-ion battery in it.

It lasted far longer if I followed the simple rule given above. My wife's ipod lasts for days of 10-hours a day use between charges as opposed to another person she knows whose ipod lasts a just a couple hours before needing a charge again. I always insist on her charging new lithium-ion batteries as above.

Then they say: UK pumped hydro storage runs out in 22 hours. Well with average of 4.5 hours 'outage' that is plenty of time.

You must also include the recharge time, which is much longer, but varies. In peak times of the year, the recharge time can be weeks. So, you get 22 hours at MAX capacity, but the reservoirs are only at max capacity if you have time to fully re-fill them. You also need to break it down regionally, because a surplus 500 miles away from where you need it doesn't do you any good.

I think we will continue to benefit most from advances in other areas that make consumer demand go down. There are several ideas being looked at which may result in greatly improved efficiency in heating and airconditioning, as well as household electronics. A good thermo-electric that works at low temperature delta, for example, would make windmills obsolete.

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